1. Field of the Invention
The present invention relates to the papermaking arts. More specifically, the present invention relates to a device for stabilizing the seam loops of a papermaker's fabric until the fabric is seamed on a paper machine.
2. Description of the Prior Art
During the papermaking process, a cellulosic fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, onto a moving forming fabric in the forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric, leaving the cellulosic fibrous web on the surface of the forming fabric.
The newly formed cellulosic fibrous web proceeds from the forming section to a press section, which includes a series of press nips. The cellulosic fibrous web passes through the press nips supported by a press fabric, or, as is often the case, between two such press fabrics. In the press nips, the cellulosic fibrous web is subjected to compressive forces which squeeze water therefrom, and which adhere the cellulosic fibers in the web to one another to turn the cellulosic fibrous web into a paper sheet. The water is accepted by the press fabric or fabrics and, ideally, does not return to the paper sheet.
The paper sheet finally proceeds to a dryer section, which includes at least one series of rotatable dryer drums or cylinders, which are internally heated by steam. The newly formed paper sheet is directed in a serpentine path sequentially around each in the series of drums by a dryer fabric, which holds the paper sheet closely against the surfaces of the drums. The heated drums reduce the water content of the paper sheet to a desirable level through evaporation.
It should be appreciated that the forming, press and dryer fabrics all take the form of endless loops on the paper machine and function in the manner of conveyors. It should further be appreciated that paper manufacture is a continuous process which proceeds at considerable speeds. That is to say, the fibrous slurry is continuously deposited onto the forming fabric in the forming section, while a newly manufactured paper sheet is continuously wound onto rolls after it exits from the dryer section.
Woven fabrics take many different forms. For example, they may be woven endless, or flat woven and subsequently rendered into endless form with a seam. Woven fabrics are typically in the form of endless loops, or are seamable into such forms, having a specific length, measured longitudinally therearound, and a specific width, measured transversely thereacross. Because paper machine configurations vary widely, paper machine clothing manufacturers are required to produce fabrics, and other paper machine clothing, to the dimensions required to fit particular positions in the paper machines of their customers. Needless to say, this requirement makes it difficult to streamline the manufacturing process, as each fabric must typically be made to order.
Fabrics in modern papermaking machines may have a width of from 5 to over 33 feet, a length of from 40 to over 400 feet and weigh from approximately 100 to over 3,000 pounds. These fabrics wear out and require replacement. Replacement of fabrics often involves taking the machine out of service, removing the worn fabric, setting up to install a fabric and installing the new fabric. While many fabrics are endless, about half of those used in press sections of the paper machines today are on-machine-seamable. Virtually all dryer fabrics have a seam. Some Paper Industry Process Belts (PIPBs) are contemplated to have an on machine seam capability, such as some transfer belts, known as Transbelt®. Installation of the fabric includes pulling the fabric body onto a machine and joining the fabric ends to form an endless belt.
A seam is generally a critical part of a seamed fabric, since uniform paper quality, low marking and excellent runnability of the fabric require a seam which is as similar as possible to the rest of the fabric in respect of properties such as thickness, structure, strength, permeability etc. In brief, the seam region of any workable fabric must behave as the body of the fabric with respect to characteristics such as permeability to water and to air, in order to prevent the periodic marking by the seam region of the paper product being manufactured on the fabric. In addition, press fabrics are subjected to compressive loads and the seam therefore must be able to withstand the repeated load/unload cycle. Despite the considerable technical obstacles presented by these requirements, it is highly desirable to develop seamable fabrics, because of the comparative ease and safety with which they can be installed.
To facilitate seaming, many current fabrics have seaming loops on the crosswise edges of the two ends of the fabric. The seaming loops themselves are formed by the machine-direction (MD) yarns of the fabric. A seam is formed by bringing the two ends of the fabric press together, by interdigitating the seaming loops at the two ends of the fabric, and by directing a so-called pin, or pintle, through the passage defined by the interdigitated seaming loops to lock the two ends of the fabric together.
Because these fabrics have a limited lifespan and require regular replacement, paper mills typically order replacement fabrics ahead of time. These fabrics may be stored in inventory for relatively long periods in the typically hot, wet conditions found in many paper mills. During shipment and storage the seam loops must be protected from damage. Further, the alignment and orientation of the seam loops can naturally shift over time due to environmental conditions and inherent forces in the fabric. Any distortion in the seam loops may result in seaming difficulties when the fabric is eventually installed. It is of primary importance that the seam be as easy to connect on the machine as possible.
All seamed fabrics exhibit some torque imbalance in their seam loops which depends, at least in part, on the weave pattern and fabric design. Various modifications to the woven base fabric patterns have been tried to prevent this imbalance from occurring. Although some of these modifications have had limited success, the seam loops still distort and tilt if the fabric ages sufficiently and the forces remain sufficiently high. Unfortunately, adjacent loops “distort” differently from one another.
Presently, following inspection but prior to shipment, a monofilament or metal wire of a certain diameter is inserted through the seam loops in both the edges of the fabric. This wire is typically referred to as a protection cable. The function of the protection cable is to prevent the seaming loops from being damaged. Since this cable is generally installed and removed as one piece, the diameter of the cable must be significantly smaller than the clearance of the loops to minimize friction and allow for the cable to pass through the loops.
Because the protection cable is of a smaller diameter than the seam loops, the loops can still move and distort in their alignment. This distortion and tilt will continue until the loops bind on the outside edges of the protection cable. The distorted loops make it difficult to interdigitate and thread a pintle through the loops to form the seam. Hence, fabrics which have been in storage for long periods often have significantly distorted seam loops which are very difficult to seam. Depending upon yarn material, form, weave pattern, etc. seam loop distortion can occur relatively soon after the seam loops are formed. An advantage of having non-deformed seam loops is the speed and ease of seaming when installing the fabric on a paper machine.
Therefore, a need exists for a method of protecting and stabilizing the orientation of the seaming loops until a fabric is ready for installation and seaming on a papermaking machine.